+ (id)newMyClass:my_needed_parameters_here...;- (id)initMyClass:my_needed_parameters_here...;...@endThen you will add object of class MyClass to the NSArray instance.If you need to insert nil references, replace them by [NSNull null]. Later, when you will retrieve objects from the NSArray or the NSDictionary instance, you can test if the object is of class NSNull with isKindOfClass or isMemberOfClass methods.